Electric driving wheel type work vehicle

ABSTRACT

An electric driving wheel type work vehicle has a traveling motor  21,  an inverter  313  for supplying the motor with three-phase power converted from DC power, a pre-driver circuit  312  for supplying a gate signal  316  to the inverter  313  on the basis of an input PWM signal, a controller  311  for outputting to the pre-driver circuit the PWM signal  315  for controlling the driving of the motor  21,  parking brake means  10,  and parking brake condition detection means  12  that detects the condition of the parking brake means  10.  When the parking brake condition detection means  12  detects the parking brake means  10  has been operated, the pre-driver circuit  312  cuts off the output of the gate signal  316,  or the input of the PWM to the pre-driver circuit  312  is cut off.

TECHNICAL FIELD

The present invention relates to a work machine that uses wheel typetraveling means, such as a wheel loader operating not only on flatlandsbut also often on slop lands in a manner involving frequent start andstop during work. More particularly, the invention relates to anelectric driving wheel type work vehicle that is driven by a motor whiletraveling.

BACKGROUND ART

The standard wheel loaders are equipped with an engine as its drivingsource and has engine power transmitted to the wheels via a torqueconverter or a gear transmission. In response to operators' manipulationof the forward/reverse lever, the wheel loader allows the geartransmission to be shifted to forward (F), to neutral (N), or to reverse(R). The wheel loaders are also furnished with a parking brake device.Activating the parking brake causes the wheel loaders to put the geartransmission in the neutral (N) position to cut off power transmissionto the wheels. This operation prevents the parking brake from draggingand inhibits the wheel loader from getting started inadvertently.

By contrast, electric driving wheel loaders have their wheels driven bythe motor. Since the motor itself can be changed in its drivingdirection and possesses a variable speed function, some vehicles of thistype are not equipped with the gear transmission. That means there is aneed for some other methods for cutting off power transmission to thewheels while the parking brake is being activated. A first known method,for example, involves an electric vehicle parking brake device having aparking brake lever that is equipped with a switch for causing a motorcontroller to detect the operating status of the parking brake on thevehicle, the switch controlling the output of power conversion means inthe motor controller (e.g., see Patent Literature 1). A second knownmethod involves an electric vehicle parking brake device having a lockdetection device that detects the condition of engagement between thelocking teeth of a parking gear attached to the motor output shaft; andthe pawls of a locking member, the lock detection device having acontroller detecting the operating status of the parking brake of thevehicle and operating a relay switch accordingly to disconnect a powersupply circuit of the motor (e.g., see Patent Literature 2).

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: JP-1994-169502-A-   Patent Literature 2: JP-1996-198067-A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The devices described in the above-cited Patent Literature 1 and 2 bothget the controller to detect the condition of the parking brake tocontrol activation and deactivation of the motor accordingly, and tocontrol motor drive in accordance with the condition of the acceleratorpedal. In a case where the controller malfunctions, it might not bepossible to cut off power transmission to the wheels even if the parkingbrake is activated. This requires providing measures for improvingreliability, such as installation of a redundant controller arrangement.

An object of the present invention is to provide an electric drivingwheel type work vehicle which, even if the controller malfunctions, cancut off power transmission to the wheels when the parking brake isactivated.

Means for Solving the Problem

(1) In achieving the above object and according to the presentinvention, there is provided an electric driving wheel type work vehiclehaving a traveling motor, an inverter for driving the motor, apre-driver circuit for supplying a gate signal to the inverter on thebasis of an input signal, a controller for outputting to the pre-drivercircuit the signal for controlling the driving of the motor, and parkingbrake means. The work vehicle includes parking brake condition detectionmeans that detects a condition of the parking brake means. When theparking brake condition detection means detects that the parking brakemeans has been operated, the pre-driver circuit cuts off an output ofthe gate signal.

In a case where the controller malfunctions, the above structure wouldallow power transmission to the wheels to be cut off when the parkingbrake is activated.

(2) Preferably, in the electric driving wheel type work vehicle statedin paragraph (1) above, the pre-driver circuit should be configured tocut off the output of the gate signal regardless of the signal outputfrom the controller to the pre-driver circuit.

(3) Preferably, the electric driving wheel type work vehicle stated inparagraph (1) above should further include a distribution circuit thatoutputs a first parking brake condition signal in accordance with theparking brake condition that has been output from the parking brakecondition detection means, the distribution circuit further outputting asecond parking brake condition signal having a predetermined delay timerelative to the first parking brake condition signal. On the basis ofthe second parking brake condition signal, the pre-driver circuit shouldpreferably cut off the output of the gate signal, or the input of a PWMsignal to the pre-driver circuit should be cut off.

(4) Preferably, in the electric driving wheel type work vehicle statedin paragraph (3) above, the pre-driver circuit should include gatesignal generation means that outputs the gate signal for controlling, onthe basis of the input PWM signal, up-down arm switching elementsconstituting the inverter. The gate signal generation means may includean inhibit terminal that stops the output of the gate signal. When thesecond parking brake condition signal is input to the inhibit terminaland the parking brake condition detection means detects the parkingbrake means has been operated, the pre-driver circuit should preferablycut off the output of the gate signal.

(5) Preferably, the electric driving wheel type work vehicle stated inparagraph (3) above should further include a gate circuit interposedbetween the controller and the pre-driver circuit, the gate circuitcutting off the input of the PWM signal to the pre-driver circuit. Whenthe second parking brake condition signal is input to the inhibitterminal and the parking brake condition detection means detects theparking brake means has been operated, the gate circuit shouldpreferably cut off the input of the PWM signal to the pre-drivercircuit.

(6) Preferably, in the electric driving wheel type work vehicle statedin paragraph (3) above, the controller should include PWM signalgeneration means that outputs the PWM signal, and a gate circuitinterposed between the PWM signal generation means and the pre-drivercircuit, the gate circuit cutting off the input of the PWM signal to thepre-driver circuit. When the second parking brake condition signal isinput to the gate circuit and the parking brake condition detectionmeans detects the parking brake means has been operated, the gatecircuit should preferably cut off the input of the PWM signal to thepre-driver circuit.

(7) Preferably, in the electric driving wheel type work vehicle statedin paragraph (1) above, the pre-driver circuit may include gate signalgeneration means that outputs the gate signal for controlling, on thebasis of the input PWM signal, up-down arm switching elementsconstituting the inverter. The gate signal generation means shouldinclude an inhibit terminal that stops the output of the gate signal.When a parking brake condition signal output from the parking brakecondition detection means is input to the inhibit terminal and theparking brake condition detection means detects the parking brake meanshas been operated, the pre-driver circuit should preferably cut off theoutput of the gate signal.

(8) Preferably, the electric driving wheel type work vehicle stated inparagraph (1) above should further include a gate circuit interposedbetween the controller and the pre-driver circuit, the gate circuitcutting off the input of the PWM signal to the pre-driver circuit. Whena parking brake condition signal output from the parking brake conditiondetection means is input to the gate circuit and the parking brakecondition detection means detects the parking brake means has beenoperated, the gate circuit should preferably cut off the input of thePWM signal to the pre-driver circuit.

(9) Preferably, in the electric driving wheel type work vehicle statedin paragraph (1) above, the controller may include PWM signal generationmeans that outputs the PWM signal, and a gate circuit interposed betweenthe PWM signal generation means and the pre-driver circuit, the gatecircuit cutting off the input of the PWM signal to the pre-drivercircuit. When a parking brake condition signal output from the parkingbrake condition detection means is input to the gate circuit and theparking brake condition detection means detects the parking brake meanshas been operated, the gate circuit should preferably cut off the inputof the PWM signal to the pre-driver circuit.

Advantageous Effect of the Invention

According to the present invention, even if the controller malfunctions,it is still possible to cut off power transmission to the wheels whenthe parking brake is activated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram showing an overallconfiguration of an electric driving wheel type work vehicle accordingto a first embodiment of the present invention.

FIG. 2 is a system configuration diagram showing a structure of anelectric drive control device used by the electric driving wheel typework vehicle according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a major structure of the electricdrive control device used by the electric driving wheel type workvehicle according to the first embodiment of the present invention.

FIG. 4 is a timing chart showing the workings of the electric drivecontrol device used by the electric driving wheel type work vehicleaccording to the first embodiment of the present invention.

FIG. 5 is another timing chart showing the workings of the electricdrive control device used by the electric driving wheel type workvehicle according to the first embodiment of the present invention.

FIG. 6 is a system configuration diagram showing a structure of anelectric drive control device used by an electric driving wheel typework vehicle according to a second embodiment of the present invention.

FIG. 7 is a system configuration diagram showing a structure of anelectric drive control device used by an electric driving wheel typework vehicle according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a major structure of the electricdrive control device used by the electric driving wheel type workvehicle according to the third embodiment of the present invention.

FIG. 9 is a system configuration diagram showing a structure of anelectric drive control device used by an electric driving wheel typework vehicle according to a fourth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Explained below with reference to FIGS. 1 to 5 are the structure and theworkings of the electric driving wheel type work vehicle according tothe first embodiment of the present invention. As an example of theelectric driving wheel type work vehicle, an electric driving wheelloader will be explained. The traveling drive system of this vehicle isa so-called electric hybrid system.

First of all, an overall configuration of the electric driving wheeltype work vehicle according to the first embodiment will be explainedwith reference to FIG. 1.

FIG. 1 is a system configuration diagram showing the overallconfiguration of the electric driving wheel type work vehicle accordingto the first embodiment of the present invention.

The traveling drive system of this vehicle includes: an engine 1; apower assist motor (M/G) 6; a power control unit (PCU) 33 that performspower conversion of the M/G 6; a low-speed high-torque traveling motor(M1) 21 and a high-speed low-torque traveling motor (M2) 22 that drivewheels 9 via a drive shaft 8 and a center joint (CJ) 15; power controlunits (PCU) 31 and 32 that respectively perform power conversion of thetraveling motors 21 and 22; a capacitor 11 serving as a secondarybattery constituting an electrical storage unit that stores the powergenerated by the M/G 6 as well as the power regenerated by the travelingmotors 21 and 22; and a bus (BUS) 35 for transferring power between thePCUs 31, 32 and 33 and the capacitor 11.

The power generated by the M/G 6 rotated by the power of the engine 1and the power regenerated by the traveling motors 21 and 22 at a time ofbraking during traveling are stored into the capacitor 11. The powerfrom the capacitor 11 is used by an electric power converter (inverter)313 to drive the traveling motors 21 and 22. Whereas the firstembodiment uses two traveling motors of different characteristics, theremay be provided only one traveling motor instead. Another alternativemay be that each of the wheels is equipped with a traveling motor. Thecapacitor adopted by the first embodiment to be explained below may bereplaced with a suitable battery serving as a secondary battery.

This system is furnished with a spring-activated parking brake 10.Turning off a parking brake switch (parking brake condition detectionmeans)(parking brake switch 12 in FIG. 2) deactivates the parking brakeby getting a hydraulic pump 4 to supply a hydraulic pressure surpassingspring force. Turning on the parking brake switch activates the parkingbrake by cutting off the hydraulic pressure from the hydraulic pump 4.

An implement 5 of this system (front structure of the wheel loader) isdriven by the hydraulic pressure from the hydraulic pump 4 rotated bythe engine 1. The implement 5 includes a bucket, a lift arm, andsteering. The hydraulic pressure supplied from the hydraulic pump 4 iscontrolled by a control valve (C/V) in a manner controlling thedirection and the flow rate of hydraulic fluid fed to a bucket cylinder,a lift cylinder, and a steering cylinder. This in turn controls thedirection and the speed of the bucket, lift arm, and steering.

Whereas the first embodiment has an electric hybrid traveling drivesystem, there may be provided alternatively an electric traveling drivesystem that runs on the power stored beforehand in the electricalstorage unit or on the power generated by solar power.

Explained next with reference to FIGS. 2 and 3 is the structure of theelectric drive control device used by the electric driving wheel typework vehicle according to the first embodiment.

FIG. 2 is a system configuration diagram showing a structure of theelectric drive control device used by the electric driving wheel typework vehicle according to the first embodiment of the invention. FIG. 3is a block diagram showing a major structure of the electric drivecontrol device used by the electric driving wheel type work vehicleaccording to the first embodiment of the invention.

As shown in FIG. 2, the parking brake switch 12 is located where theoperator can manipulate it, such as on an operation panel. Turning onthe parking brake switch 12 closes a solenoid valve 14 cutting off aparking brake deactivation hydraulic pressure 41 to activate the parkingbrake. Turning off the supply parking brake switch 12 opens the solenoidvalve 41 supplying the parking brake deactivation hydraulic pressure 41to deactivate the parking brake.

The power control unit (PCU) 31 includes a controller 311 that performsdrive control of the traveling motor 21 on the basis of a torque commandfrom a hybrid integrated controller (HCU) 30, an electric powerconverter (inverter) 313 that performs power conversion between the bus35 and the traveling motor 21, and a pre-driver circuit 312 thatgenerates a gate signal 316 to be input to the electric power converter313. The pre-driver circuit 312 outputs three-phase up-down arm gatesignals 316 to the electric power converter 313 on the basis of athree-phase PWM signal 315 output from the controller 311. The electricpower converter 313 performs drive control of the traveling motors 21and 22.

The PCU 31 further includes a distribution circuit 314 that distributesthe signal of the parking brake switch 12 to the controller 311 andpre-driver circuit 312. The distribution circuit 314 outputs a parkingbrake condition “a” signal 317 to the controller 311 and a parking brakecondition “b” signal 318 to the pre-driver circuit 312. At a time ofinput of the parking brake condition “a” signal 317 indicating that theparking brake switch 12 is turned on from the OFF state, the controller311 stops the output of the PWM signal 315. Also, at a time of input ofthe parking brake condition “b” signal 318 indicating that the parkingbrake switch 12 is turned on from the OFF state, the pre-driver circuit312 stops the output of the gate signals 316.

An internal structure of the pre-driver circuit 312 will be explainedbelow with reference to FIG. 3.

The pre-driver circuit 312 includes a gate signal generation IC 312A.The electric power converter 313 shown in FIG. 2 has switching elementstherein for each of three phases of an up-down arm. That is, theelectric power converter 313 is equipped with six switching elements forthe three phases. Thus the pre-driver circuit 312 outputs six gatesignals 316. Meanwhile, the pre-driver circuit 312 is fed with three PWMsignals 315 from the controller 311. Thus the pre-driver circuit 312 isequipped with three gate signal generation IC's 312A, only one of whichis shown in the drawing.

At a time of input of a single PWM signal 315, the gate signalgeneration IC 312A outputs two gate signals 312 on the basis of theinput signal. A first gate signal 316 may be input to the gate terminalof a U-phase up-arm switching element in the electric power converter313 for example, and a second gate signal 316 may be input to the gateterminal of a U-phase down-arm switching element in the electric powerconverter 313, for example.

The gate signal generation IC 312A is furnished with an inhibit terminalINH. The parking brake condition “b” signal 318 is input to the inhibitterminal INH. When the parking brake switch 12 is turned on from the OFFstate, the parking brake condition “b” signal 318 is switched to the lowlevel from the high level. When the signal level of the inhibit terminalINH is switched to the low level, the gate signal generation IC 312Astops the output of the gate signal 316.

As will be discussed later with reference to FIG. 5, when the parkingbrake switch 12 is turned on from the OFF state, a delay time Td isinserted into the parking brake condition “b” signal 318. The delay timeTd is set to be longer than the time during which the controller 311stops driving of the traveling motor 21.

The HCU 30 also measures the parking brake deactivation hydraulicpressure 41 by use of a pressure sensor 42, so as to detect activationand deactivation of the parking brake 10. Thus when the controller 311notifies the HCU 30 of the condition of the parking brake condition “a”signal 317 allowing the HCU 30 to match the notification to thecondition of the parking brake 10 obtained by the pressure sensor 42, itis possible to detect malfunction of the distribution circuit 314.

Explained below with reference to FIGS. 4 and 5 is how the electricdrive control device used by the electric driving wheel type workvehicle according to the first embodiment operates.

FIGS. 4 and 5 are timing charts showing the workings of the electricdrive control device used by the electric driving wheel type workvehicle according to the first embodiment.

FIG. 4 shows the workings of the electric drive control device, in casethat the parking brake is operated in the normal state. In FIG. 4, thehorizontal axis denotes time. The vertical axis stands for the conditionof the parking brake switch 12 in FIG. 4(A), for the condition of theparking brake 10 in FIG. 4(B), and for the condition of the parkingbrake condition “a” signal 317 in FIG. 4(C). The vertical axis standsfor the PWM signal 315 in FIG. 4(D), for the condition of the parkingbrake condition “b” signal 318 in FIG. 4(E), and for the condition ofthe gate signal 316 in FIG. 4(F).

Once the parking brake switch 12 is turned on at time t1 as shown inFIG. 4(A), the parking brake 10 transitions from the deactivated stateto the activated state as indicated in FIG. 4(B). Once the parking brakecondition “a” signal 317 input via the distribution circuit 314 isturned on from the OFF state as shown in FIG. 4(C), the controller 311in the PCU 31 starts controlling activation and deactivation of thetraveling motor 21, and stops the output of the PWM signal 315 at timet2 as depicted in FIG. 4(D). This allows the pre-driver circuit 312 tostop the output of the gate signal 316 on the basis of activation anddeactivation control of the controller 311 before the parking brakecondition “b” signal 318 input via the distribution circuit 314 isturned on from the OFF state (at time t3) following the delay time Td.

Moreover, as shown in FIG. 4(A), once the parking brake switch 12 isturned off at time t4 as shown in FIG. 4(A), the parking brake 10transitions from the activated state to the deactivated state asindicated in FIG. 4(B). Once the parking brake condition “a” signal 317input via the distribution circuit 314 is turned off from the ON stateas shown in FIG. 4(C), the controller 311 in the PCU 31 restarts drivecontrol of the traveling motor 21 at time t5 and outputs the PWM signal315 as depicted in FIG. 4(D). Once the parking brake condition “b”signal 318 input via the distribution circuit 314 is turned off from theON state as shown in FIG. 4(E), the pre-driver circuit 312 can restartthe output of the gate signal 316 at time t5 on the basis of drivecontrol of the controller 311 as indicated in FIG. 4(F).

In the manner described above, the electric drive control device of thefirst embodiment can stop and restart traveling drive on the basis ofthe operations of the parking brake.

FIG. 5 shows the workings of the electric drive control device, in casethat the parking brake is operated with the controller 311 in anabnormal state. The horizontal axis in FIG. 5 denotes time. The verticalaxes in FIGS. 5(A) through 5(F) are the same as those in FIGS. 4(A)through 4(F).

When the parking brake switch 12 is turned on at time t1 as shown inFIG. 5(A), the parking brake 10 transitions from the deactivated stateto the activated state as indicated in FIG. 5(B). It is assumed herethat, as shown in FIG. 5(C), even when the parking brake condition “a”signal 317 input via the distribution circuit 314 has been turned onfrom the OFF state, the controller 311 in the PCU 31 remains in theabnormal state where it is incapable of stopping drive control of thetraveling motor 21.

In that case, as shown in FIG. 5(E), when the parking brake condition“b” signal 318 input via the distribution circuit 314 is turned on fromthe OFF state at time t3 following the delay time Td, the pre-drivercircuit 312 is capable of stopping the output of the gate signal 316 onthe basis of the parking brake condition “b” signal 318 even if thecontroller 311 keeps outputting the PWM signal, as indicated in FIG.5(F).

Thereafter, with the controller 311 restarted by key operation, the actof turning off the parking brake switch 12 at time t4 causes the parkingbrake 10 to transition from the activated state to the deactivatedstate. When the parking brake condition “a” signal 317 input via thedistribution circuit 314 is turned off from the ON state, the controller311 in the PCU 31 restarts drive control of the traveling motor 21 andoutputs the PWM signal 315 (at time t5). Because the parking brakecondition “b” signal 318 input via the distribution circuit 314 isturned off from the ON state, the pre-driver circuit 312 can restart theoutput of the gate signal 316 on the basis of drive control of thecontroller 311.

In the manner described above, even in a case where the controller 311is in the abnormal state, the electric drive control device of the firstembodiment would be able to stop and restart traveling drive on thebasis of the operations of the parking brake.

According to the method described in the above-cited Patent Literature1, there is provided a relay switch that cuts off the power supplycircuit for the motor. Since the power to be supplied to the travelingmotor of the wheel loader is high, the relay switch needs to be of highcapacity, which contributes to increasing cost. According to the firstembodiment, by contrast, the gate signal to the motor driving circuit iscut off to discontinue power transmission to the wheels. This eliminatesthe need for the high-capacity relay switch designed to turn off themotor power supply circuit. With no need for such a switch, the cost ofthe electric driving wheel type work vehicle will be reduced.

Explained next with reference to FIG. 6 is how the electric drivingwheel type work vehicle according to the second embodiment of theinvention is structured and how it operates. The overall configurationof the electric driving wheel type work vehicle according to the secondembodiment is the same as that shown in FIG. 1.

FIG. 6 is a system configuration diagram showing a structure of anelectric drive control device used by the electric driving wheel typework vehicle according to the second embodiment of the presentinvention. In FIG. 6, the same reference numerals as those used in FIG.2 suggest the same or corresponding parts.

In addition to the configuration shown in FIG. 1, the second embodimenthas a gate circuit 31G interposed between the controller 311 and thepre-driver circuit 312. The parking brake condition “b” signal 318output from the distribution circuit 314 is input to the gate circuit31G.

There are three PWM signals 315 to be input from the controller 311 tothe gate circuit 31G. The gate circuit 31G may be furnished with threetwo-input AND gates, for example. One PWM signal 315 is fed to one ofthe two inputs of each AND gate, and the parking brake condition “b”signal 318 is fed to the other input of the AND gate. Thus when theparking brake condition “b” signal 318 transitions from the high levelto the low level, the AND gate in question is turned off, which cuts offthe input of the PWM signal 315 from the controller 311 to thepre-driver circuit 312.

In the second embodiment, as with the first embodiment, in a case wherethe parking brake is operated with the controller 311 in the abnormalstate and where the parking brake condition “b” signal 318 input via thedistribution circuit 314 is turned on from the OFF state following thedelay time Td, the input of the PWM signal 315 to the pre-driver 312would be cut off even if the controller 311 keeps outputting the PWMsignal 315. In this manner, the output of the gate signal 316 would bestopped.

As described above, even in a case where the controller 311 is in theabnormal state, the electric drive control device of the secondembodiment would still be able to stop and restart traveling drive onthe basis of the parking brake operations.

Explained next with reference to FIGS. 7 and 8 is how the electricdriving wheel type work vehicle according to the third embodiment of thepresent invention is structured and how it operates. The overallconfiguration of the electric driving wheel type work vehicle accordingto the third embodiment is the same as that shown in FIG. 1. FIG. 7 is asystem configuration diagram showing a structure of an electric drivecontrol device used by the electric driving wheel type work vehicleaccording to the third embodiment of the present invention. In FIG. 7,the same reference numerals as those used in FIG. 2 designate the sameor corresponding parts. FIG. 8 is a block diagram showing a majorstructure of the electric drive control device used by the electricdriving wheel type work vehicle according to the third embodiment of theinvention.

In the third embodiment, as shown in FIG. 7, the parking brake condition“b” signal 318 output from the distribution circuit 314 is input to acontroller 311′.

An internal structure of the controller 311′ will be explained next withreference to FIG. 8. The controller 311′ includes a PWM signalgeneration circuit 311A that generates the PWM signal 315. The generatedPWM signal 315 is input to the pre-driver circuit 312 shown in FIG. 7.Inside the controller 311′, a gate circuit 311G is interposed betweenthe PWM signal generation circuit 311A and the pre-driver circuit 312.The parking brake condition “b” signal 318 output from the distributioncircuit 314 is input to the gate circuit 311G.

There are three PWM signals 315 to be input to the gate circuit 311Gfrom the controller 311′. The gate circuit 311G may include threetwo-input AND gates, for example. One PWM signal 315 is fed to one ofthe inputs of each AND gate. The parking brake condition “b” signal 318is fed to the other input of the AND gate. Thus when the parking brakecondition “b” signal 318 transitions from the high-level to thelow-level, the AND gate is turned off, which cuts off the input of thePWM signal 315 to the pre-driver 312 from the controller 311′.

In the third embodiment, as with the first embodiment, in a case wherethe parking brake is operated with the controller 311′ in the abnormalstate and where the parking brake condition “b” signal 318 input via thedistribution circuit 314 is turned on from the OFF state following thedelay time Td, the input of the PWM signal 315 to the pre-driver 312would be cut off even if the controller 311′ keeps outputting the PWMsignal 315. In this manner, the output of the gate signal 316 would bestopped.

As described above, even in a case where the controller 311′ is in theabnormal state, the electric drive control device of the thirdembodiment would still be able to stop and restart traveling drive onthe basis of the parking brake operations.

Explained next with reference to FIG. 9 is how the electric drivingwheel type work vehicle according to the fourth embodiment of thepresent invention is structured and how it operates. The overallconfiguration of the electric driving wheel type work vehicle accordingto the fourth embodiment is the same as that shown in FIG. 1.

FIG. 9 is a system configuration diagram showing a structure of anelectric drive control device used by the electric driving wheel typework vehicle according to the fourth embodiment of the presentinvention. In FIG. 9, the same reference numerals as those used in FIG.2 designate the same or corresponding parts.

The fourth embodiment is characterized by the absence of thedistribution circuit 314 shown in FIG. 2. The signal from the parkingbrake switch 12 is therefore input unchecked to the pre-driver circuit312 as the parking brake condition “b” signal 318.

That is, in the fourth embodiment, upon input of the parking brakecondition “b” signal 318 indicating that the parking brake switch 12 isturned on from the OFF state, the pre-driver circuit 312 stops theoutput of the gate signal 316. Meanwhile, without the distributioncircuit 314 shown in FIG. 2, even if the parking brake switch 12 isturned on from the OFF state, the controller 311 will not stop theoutput of the PWM signal 315. Even in a case where the parking brake isoperated with the controller 311 in the abnormal state, the pre-drivercircuit 312 still would stop the output of the gate signal 316.

Alternatively, as in the embodiment shown in FIG. 6, there may beprovided a gate circuit 31G indicated by a broken line. The parkingbrake condition “b” signal 318 indicated by a dashed line is input tothe gate circuit 31G instead of to the pre-driver circuit 312. Also inthe manner explained above with reference to FIG. 6, it is possible tocut off the input of the PWM signal 315 to the pre-driver circuit 312.

As in the embodiment shown in FIG. 7, the parking brake condition “b”signal 318 indicated by the dashed line can be input to the controller311. The controller 311 includes the gate circuit 311G as shown in FIG.8. Also in the manner explained above with reference to FIG. 8, it ispossible to cut off the input of the PWM signal 315 to the pre-drivercircuit 312.

In the fourth embodiment, as with the first embodiment, in a case wherethe parking brake is operated with the controller 311 in the abnormalstate and where the parking brake condition “b” signal 318 input via thedistribution circuit 314 is turned on from the OFF state, the output ofthe PWM signal 315 from the pre-driver 312 would be stopped even if thecontroller 311 keeps outputting the PWM signal 315.

As described above, even in a case where the controller 311 is in theabnormal state, the electric drive control device of the fourthembodiment would still be able to stop and restart traveling drive onthe basis of the parking brake operations.

Although the embodiments were discussed above by use of examples inwhich the PWM signal 315 is continuously output to the pre-drivercircuit 312 when the controller 311 or 311′ is in the abnormal state,this is not limitative of the present invention. As another example, thenormality or abnormality of the controller 311 or 311′ may be identifieddepending on the magnitude of the PWM signal 315.

DESCRIPTION OF REFERENCE CHARACTERS

-   10 Parking brake-   12 Parking brake switch-   31 Power control unit (PCU)-   311, 311′ Controller-   312 Pre-driver circuit-   313 Electric power converter (inverter)-   314 Distribution circuit-   315 Three-phase PWM signal-   316 Gate signal-   317 Parking brake condition “a” signal-   318 Parking brake condition “b” signal-   31G, 311G Gate circuit

1. An electric driving wheel type work vehicle having a traveling motor,an inverter for driving the motor, a pre-driver circuit for supplying agate signal to the inverter on the basis of an input signal, acontroller for outputting to the pre-driver circuit the signal forcontrolling the driving of the motor, and parking brake means, theelectric driving wheel type work vehicle comprising: parking brakecondition detection means that detects a condition of the parking brakemeans; wherein, when the parking brake condition detection means detectsthat the parking brake means has been operated, the pre-driver circuitcuts off an output of the gate signal.
 2. The electric driving wheeltype work vehicle according to claim 1, wherein the pre-driver circuitcuts off the output of the gate signal regardless of the signal that isoutput from the controller to the pre-driver circuit.
 3. The electricdriving wheel type work vehicle according to claim 1, further comprisinga distribution circuit that outputs a first parking brake conditionsignal in accordance with the parking brake condition that has beenoutput from the parking brake condition detection means, thedistribution circuit further outputting a second parking brake conditionsignal having a predetermined delay time relative to the first parkingbrake condition signal; wherein, on the basis of the second parkingbrake condition signal, the pre-driver circuit cuts off the output ofthe gate signal, or an input of a PWM signal to the pre-driver circuitis cut off.
 4. The electric driving wheel type work vehicle according toclaim 3, wherein the pre-driver circuit includes gate signal generationmeans that outputs the gate signal for controlling, on the basis of theinput PWM signal, up-down arm switching elements constituting theinverter; wherein the gate signal generation means includes an inhibitterminal that stops the output of the gate signal; and wherein, when thesecond parking brake condition signal is input to the inhibit terminaland the parking brake condition detection means detecting activation ofthe parking brake means detects the parking brake means has beenoperated, the pre-driver circuit cuts off the output of the gate signal.5. The electric driving wheel type work vehicle according to claim 3,further comprising a gate circuit interposed between the controller andthe pre-driver circuit, the gate circuit cutting off the input of thePWM signal to the pre-driver circuit; wherein, when the second parkingbrake condition signal is input to the inhibit terminal and the parkingbrake condition detection means detects the parking brake means has beenoperated, the gate circuit cuts off the input of the PWM signal to thepre-driver circuit.
 6. The electric driving wheel type work vehicleaccording to claim 3, wherein the controller includes PWM signalgeneration means that outputs the PWM signal, and a gate circuitinterposed between the PWM signal generation means and the pre-drivercircuit, the gate circuit cutting off the input of the PWM signal to thepre-driver circuit; and wherein, when the second parking brake conditionsignal is input to the gate circuit and the parking brake conditiondetection means detects the parking brake means has been operated, thegate circuit cuts off the input of the PWM signal to the pre-drivercircuit.
 7. The electric driving wheel type work vehicle according toclaim 1, wherein the pre-driver circuit includes gate signal generationmeans that outputs the gate signal for controlling, on the basis of theinput PWM signal, up-down arm switching elements constituting theinverter; wherein the gate signal generation means includes an inhibitterminal that stops the output of the gate signal; and wherein, when aparking brake condition signal output from the parking brake conditiondetection means is input to the inhibit terminal and the parking brakecondition detection means detects the parking brake means has beenoperated, the pre-driver circuit cuts off the output of the gate signal.8. The electric driving wheel type work vehicle according to claim 1,further comprising a gate circuit interposed between the controller andthe pre-driver circuit, the gate circuit cutting off the input of thePWM signal to the pre-driver circuit; wherein, when a parking brakecondition signal output from the parking brake condition detection meansis input to the gate circuit and the parking brake condition detectionmeans detects the parking brake means has been operated, the gatecircuit cuts off the input of the PWM signal to the pre-driver circuit.9. The electric driving wheel type work vehicle according to claim 1,wherein the controller includes PWM signal generation means that outputsthe PWM signal, and a gate circuit interposed between the PWM signalgeneration means and the pre-driver circuit, the gate circuit cuttingoff the input of the PWM signal to the pre-driver circuit; and wherein,when a parking brake condition signal output from the parking brakecondition detection means is input to the gate circuit and the parkingbrake condition detection means detects the parking brake means has beenoperated, the gate circuit cuts off the input of the PWM signal to thepre-driver circuit.